This invention relates to the recovery of bituminous coal by flotation. More particularly, the invention is directed to a reagent for treating a solid material disposed in a liquid medium and having an oxygen-controlled surface condition. The reagent may be used in froth flotation equipment and in other types of continuous and batch flotation processes.
Bituminous coal is a porous material in which environmental gases, such as air, may be entrapped. There are volatile surface products in the coal which unite with oxygen on the surface of a coal particle. There is inorganic material generally referred to in the industry as ash content and includes oxides, carbonates and silicates. All of these factors contribute to the basic problem of an oxygen-controlled surface condition being present on particulate bituminous coal. It is well known in the coal flotation industry, that coal having an oxygen-controlled surface condition will not be wetted by liquid hydrocarbons which are normally used in coal flotation. Consequently, large amounts of coal have not been recovered but have been carried into the refuse ponds and piles wherever there has been a coal production facility.
Froth flotation processes and equipment have been used for many years in the coal recovery industry. Much agitation, both mechanically and through the use of bubbling air, is used to effect the desired flotation. In other words, the environment within which the coal is being treated for flotation is also filled with ogygen. Thus, the environment within the froth flotation process contributes significantly to the maintaining of the oxygen-controlled surface condition on the bituminous coal fines.
The bituminous coal also includes pyritic sulfur and organic sulfur. The presence of a high sulfur content in the coal causes it to become a low grade material which may cause unwanted sulfur compounds being released into the atmosphere when the coal is burned. Further, the coal cannot be used with such high sulfur contents for applications such as C-coal which is a high grade metallurgical coal. The presence of the sulfur in the coal effects the formation of sulfuric acid when the coal is mixed with water. The longer the coal stands in the water, the more acid the water becomes. The acid water effluent is difficult to dispose of. It is a particular problem where such an effluent is being dumped into water tributaries and streams.
Over the years, large deposits of unrecovered coal, flowing from froth flotation processes, has been collected in huge refuse ponds. These ponds may be totally below ground or have been collected in containers above ground. Literally, millions of tons of coal having an oxygen-controlled surface condition lies in these ponds. Vast amounts of the unrecovered bituminous coal is also collected in large piles subjected to the open atmosphere.
It is possible to recover fine coal, that is ten-mesh or finer, in conventional hydrocyclone systems. This conventional type of system, collects the coal fines on the basis of specific gravity or bulk density. It is emphasized, however, that the bituminous coal fines will have an oxygen-controlled surface condition and a relatively high sulfur content. Thus, the ash content and attendant problems of burning such coal will be associated with this type of recovery. That is, the oxygen-controlled surface condition and high sulfur content will have an adverse effect upon the coal used in any subsequent products. For example, it would not be useful for use as metallurgical coal and is doubtful whether it would be usable for making coke.
The U.S. Pat. Nos. 1,156,041, 1,425,187, 1,593,232, 2,198,915 and 2,492,936, disclose various types of reagents, bath flotation systems and froth flotation processes using various types of reagents. All of these prior art reagents operate in the presence of high oxygen environmental conditions, both from a chemical and a mechanical standpoint. Chemically, the reagents incorporate the use of combined oxygen. Mechanically, the bubbling of air aggravates the oxygen-controlled surface condition on the bituminous coal fines. While the prior art makes reference to the cleaning of the oxide from the surface of sulfide particles with sulfuric acid, such a cleaning is deemed not chemically possible. Also, the prior art processes are designed, generally, to avoid the formation of hydrogen sulfide during the process of concentrating mineral ores by flotation. Various other distinctions over the prior art flotation techniques will be evident as the present invention is described herein.